The present invention relates to hot melt adhesives, and more specifically to hot melt adhesives having antimicrobial properties and which find usefulness in the manufacture of disposable nonwoven articles.
Nonwoven fabric is comprised of an interlocking fiber network, and is employed in the construction of disposable goods. Specific applications of nonwovens have included disposable diapers, sanitary napkins, surgical drapes, hospital pads and adult incontinence products.
In such applications it is generally necessary to adhere nonwoven, tissue, absorbent fluff or the like to another substrate. This second substrate may be another nonwoven fabric, tissue, or a material such as a polyolefin e.g. a polyethylene or polypropylene layer. Typically, a hot melt adhesive has been used to bond such materials together since there is no evaporation step necessary during manufacture, as would be the case for water-based or solvent-based adhesives. Suitable hot melt adhesives must possess the appropriate bond strength to adhere the substrates involved, and must also possess good flexibility, no staining or bleed through, suitable viscosity and open time to function on commercial equipment, acceptable stability under storage conditions, and acceptable thermal stability under normal application conditions.
Many different polymers have been used in hot melt adhesives employed in the construction of disposable nonwoven goods. In this regard typical hot melt adhesives have employed polymers which have included polybutene-1 (homopolymer and copolymer); S-I-S (styrene-isoprene-styrene) block copolymer; SBS (styrene-butadiene-styrene) block copolymer; SEBS (styrene-ethylene-butylene-styrene) block copolymer; EVA (ethylene vinyl acetate); and APAO (amorphous poly alpha olefin). These polymers, when properly blended, provide acceptable adhesion between most substrates employed in typical nonwoven construction such as diapers.
One noteworthy concern of prior hot melt adhesives used in the above-noted nonwoven applications is the lack of protection against the direct or indirect effects by microorganisms which could change the properties, appearance or odor of the adhesive and/or nonwoven article. Therefore, it would be desirable to have a hot melt adhesive which is useful for bonding to substrates which are typically employed in the construction of nonwoven articles, such as polyethylene, polypropylene, nonwoven, tissue, or fluff, and which further provides hygienic properties by inhibiting or preventing growth of bacteria which often is accompanied by a change in adhesion properties, color formation and odor development.
It is therefore an object of the present invention to provide an improved hot melt adhesive which is useful for the manufacture of disposable nonwoven articles.
A further object of the present invention is to provide a hot melt adhesive which can be employed as a construction adhesive which further provides hygienic properties to disposable nonwoven articles.
In order to accomplish the above objects, the present invention provides a hot melt adhesive having the following composition (by weight):
about 10-80% of a polymer;
about 20-70% of a tackifying resin;
about 0-50% of a plasticizer;
about 0-50% of a wax;
about 0.1-5% of an antioxidant; and
about 0.01-5% of a bacteriostat, the components totaling 100% by weight.
The bacteriostat must be reasonably compatible with the other raw materials used in the hot melt adhesive so that it does not adversely affect the construction performance or the thermal stability of the adhesive. The bacteriostat also should not contain any water or other solvents so that it is readily processable in hot melt mixing equipment, and also should be non-toxic for the end user.
Such criteria is accomplished by the incorporating into an adhesive a compound of the formula: 
wherein X1 is a member selected from the group consisting of chlorine and bromine, X2 is a member selected from the group consisting of chlorine and bromine, and X3 is a member selected from the group consisting of hydrogen and chlorine. When each of X1, X2 and X3 represents chlorine, the compound is triclosan, which is the preferred bacteriostat.
The adhesives of the instant invention thus provide excellent growth-inhibiting action against bacteria, and are especially suited for use in absorbent products such as diapers, training pants, incontinent products, feminine care products, and medical products. With all of these products there is a need to bond the layers or substrates of the article together and hot melts are often used as discussed above. Usually the core area of the article is adhered by spraying a layer of adhesive onto a nonwoven substrate and adhering it to an absorbent core. In many cases, a layer of tissue is placed between the nonwoven and the core, sometimes fully wrapping the core and in other cases simply covering the top or bottom layer. Another layer of adhesive may be used to bond the absorbent core fluff to the tissue and further another layer of adhesive may bond the tissue or fluff to the backsheet (which is often polyethylene or a composite laminate). So there is at least one and often a number of layers of sprayed hot melt used in bonding the core into place, and these multiple layers of adhesive, all or any combination of which may contain the bacteriostat ingredient, provide an excellent environment in which microorganisms, and particularly bacteria, may be controlled.
In another aspect of the invention, there is provided an antimicrobial, sprayable, thermoplastic polymer composition comprising a blend of about 95-99.99% by weight of a thermoplastic polymer, said thermoplastic polymer having a melt index greater than about 100, and about 0.01-5% by weight of a bacteriostat, and where the composition has a viscosity of less than about 50,000 cP at 350xc2x0 F. Preferably, the polymer has a melt index greater than about 500, and the composition has a viscosity less than about 20,000 cP. Most preferably, the polymer has a melt index greater than about 1,000, and the composition has a viscosity less than about 10,000 cP. For certain applications and/or desired end uses, there may be no need to blend a tackifying resin, plasticizer, wax or antioxidant with the polymer. This depends upon the inherent properties of the polymer, the desired end use, and other factors typically considered by those skilled in the art.